Unauthorized copying of sensitive information has occurred since man has been storing and tracking information on documents. Combating document fraud and protecting printed content is a multi-disciplinary and international concern. The constant improvement of modern scanners with digital signal processing means and color copiers has made it economically feasible to reproduce almost perfect reproductions of currency and fraudulent travel documents. This same technology is now used everyday to easily copy printed information for nefarious reasons.
Many different security printing techniques have been developed to alert a casual observer of a fraud attempt at the time of general inspection. We refer to these technologies in general terms as “copy evident.” While these “copy evident” techniques provide some level of warning on a copy, they do not prevent someone from identifying, copying, and sharing valuable private and confidential information.
One known technique of inhibiting unauthorized copying of original documents utilizes a metallized reflective substrate on which information can be printed. When the original document is photocopied, the reflective surface of the substrate induces a predominantly black and illegible copy. In particular, the reflective surface, which forms a background for the printed information, provides a corresponding black copy background, thereby making the printed information unreadable on the document copy. Unfortunately, today's photocopiers can be manipulated to at least partially produce printed images on metallic surfaces. In addition, since incident light reflects off a polished smooth surface on a parallel plane, the mere use of a highly reflective metallic background to protect highly absorbent printed information does not effectively work with diffused photocopy devices, which capture diffused light rays. Also, the reflective substrate surface creates a high gloss or glare that provides poor contrast, thereby making it difficult to read the information on the original document and contributing to eye fatigue when reading the information.
In order to improve the security of such documents and to improve the readability of such information, it is known to provide a partially transparent screen, which is formed by randomly printing light absorbing elements over the reflective substrate. As a result, the randomly printed screen reduces the glare from the reflective substrate to provide the necessary contrast between the information and the reflective substrate. The randomly printed screen also provides a light absorption and diffraction phenomenon that, when printed in correct density and contrast, turns a photocopy of the document predominantly black.
Although the use of a randomly printed screen reduces the glare from a reflective substrate surface, which would otherwise render the information printed on the document difficult to read, this screen must be printed very dark to ensure that a resulting document copy is unreadable. Thus, the information on the original document may still be difficult to read to some extent. In essence, the readability of the information on the original document must be balanced against the security that the document provides against unauthorized copying. That is, as the screen is printed darker, document security is increased, but readability of the information on the original document is decreased. As the screen is printed lighter, the readability of the information on the original is increased, but the document security is decreased.
There, thus, remains a need to provide a document that is more readable when viewing an original of the document, yet prevents or, at the least, deters copying of information contained on such document.